Antenna feed modulation unit for ridged waveguide



Feb. 5, 1957 c. E. VOGELEY, JR., ETAL 2,780,783

ANTENNA FEED MODULATION UNIT FOR RIDGED WAVEGUIDE Filed Nov. 20, 1955"MU 20 I 16' INVENTORS Uydaii MayeleyJnQ! liz'c/zardfl Z1 6 ATTORNEYSANTENNA FEED MODULATION UNIT FOR GED WAVEGUIDE Application November 20,1953, Serial No. 393,531

(Jlaims. (Cl. 332-52) This invention relates to a method and apparatusfor achieving modulation in the antenna stage of a high frequencytransmitter or receiver employing ridged waveguides.

Although previously disclosed modulation units have been shown tooperate satisfactorily, they have also proven themselves difficult toinstall and adjust, primarily because of the close electrical andphyical tolerances imposed by the ridged waveguides employed. In thepreviously disclosed units modulation is achieved in a stage precedingthe antenna stage and utilizes a tuned probe to which a signal generatorand a modulating device are capacitatively coupled. Variations in thedimensions of the ridged portion of the waveguide in the region near theprobe produce marked difierences in the operation of the modulationunits which are difiicult to overcome. Secondly, in the installation ofthe probe a small amount of solder at the joint between the probe andthe ridge often proves to be disastrous. Furthermore, adjustment of thecoupling between the probe and the modulating device (usually agermanium welded contact crystal) is also critical. Many of thesedifficulties could be easily overcome were it not for the small physicaldimensions required of the ridged waveguide.

It is an object of this invention, therefore, to overcome thedeficiencies of the prior systems by providing a system which achievesmodulation in the antenna stage of a transmitter, rather than in anypreceding stage. Such a system has the advantages of eliminating themodulation stage of the prior art systems, and at the same timeeffecting modulation in the open region of the antenna stage whereinstallation and adjustment are more easily achieved.

A further object of this invention is the provision of a transmittingsystem employing ridged waveguides in which modulation is accomplishedin the antenna stage by means of a modulation device coupled to thedipoles of the antenna.

A still further object of this invention is the elimination of probesemployed in the modulation stage of prior art devices, and thuseliminating the inaccuracies and losses caused thereby.

Other objects and advantages of this invention, as well as itsconstruction, arrangement and operation, will be apparent from thefollowing description and claims taken in connection with theaccompanying drawing in which:

Fig. l is a schematic representation showing the inventive conceptinvolved in the system;

Fig. 2 is an isometric view showing the antenna feed employed in Fig. 1;

Fig. 3 is an isometric view showing a multiple type antenna feedconsisting of four ridged waveguides which may be utilized in thisinvention; and

Fig. 4 is an isometric view showing a standard waveguide feed on whichthis invention may be employed.

Referring now to the drawing, and particularly to Figs. 1 and 2, thereis shown a ridged waveguide 10 having a Sttes atent Patented Feb. 5, 1957 12 is mounted in conductive relationship with the waveguide 10 in anyconvenient manner in the area under the ridged portion of the waveguide.A first dipole element 13 is mounted on the mounting block inelectrically conductive relationship therewith. The second dipoleelement 14 is similarly mounted on the block 12, but is insulatedtherefrom by means of an insulating sleeve 15. A conventional reflector16 is mounted in any suitable manner in the position shown, and thewaveguide is grounded at any convenient location 17. A variableimpedance device such as the germanium welded contact crystal 18 isconnected at one end to the insulated dipole element 14 and at its otherend to the other dipole element 13 through the grounded waveguide. Amodulating signal is impressed across the crystal 18 from the signalgenerator 19, through the R. F. choke 20.

With the foregoing arrangement, a variation in the impedance of thecrystal 18 is reflected into the dipole elements 13 and 14, therebychanging the electrical aspects of the dipole array and thus modulatinga received or transmitted signal. For optimum performance of the systemit has been determined that the height of the dipole elements 13 and 14,and the spacing therebetween, should be a quarter wave length. Thedistance between the dipole element 14 and the waveguide 10 also affectsthe operation of the system. It should be noted, however, thatsatisfactory operation of the array can be achieved without criticaladjustments. In fact, with no variable coupling between the crystal 18and the dipole, with no attention being given to the length of thedipole, and with a crystal chosen at random, a modulation percentage wasachieved which in the previously known modulation systems, could only bedetected after careful and elaborate adjustments are made.

In Fig. 3 there is disclosed another antenna feed arrangement on whichthis modulation system may be employed. There is shown a multiple feedconsisting of four ridged waveguides, 21, 22, 23, and 24. The dipoleelements 25 and 26, which are associated with the wave guide 21, aremounted on a common conductive block 27 with the dipole elements 28 and29, which are associated with the waveguide 24. Similarly, the dipoleelements 30, 31, 32 and 33 are mounted on the block 34. As in Fig. 2,the dipole elements 26, 29, 31 and 33 are insulated from the conductiveblocks by means of the insulating sleeves 35 and 36.

The modulation system has also been employed on the standard waveguidefeed shown in Fig. 4. In this arrangement, a waveguide 37, having arectangular cross section is employed. The dipole elements 38, 39, 40and 41 are mounted, as shown on the conductive block 42 and one elementof each dipole is insulated therefrom by the insulating sleeves 43 and44. While the advantages of modulating in the antenna stage of a systememploying a standard waveguide, such as shown in Fig. 4, are not asapparent as in systems employing ridged waveguides, since the dimensionsof the standard waveguide are not so limited, a sufiicient advantage isobtained to justify the use of the system with this type ofinstallation. The adjustments necessary in ridged systems, while not socritical in standard systems, are still required in the use of the priorart probe devices for obtaining modulation in the standard systems, andare obviated by the use of this invention.

In summary, therefore, it is seen that this invention moves themodulation process from the interior of the waveguides, where physicalconfines render adjustment and installation difiicult, to the openregion of the antenna feed, thereby rendering installations andadjustment relatively less difficult. The system achieves modulationwithout critical adjustments necessary in the prior art devices, and itis relatively free from waveguide errors. Inasmuch as the presence ofthe extra probe employed in the prior art systems accounts for a finiteloss, its elimination reduces these losses. The system can be usedadvantageously on any known antenna feed system.

While preferred embodiments of this invention have been described itwill be obvious to those skilled in the art that various changes andmodifications may be made therein without departing from the spirit ofthe invention, and it is the intent, therefore, to cover all suchchanges and modifications as fall within the true spirit and scope ofthe invention.

What is claimed is:

1. An antenna feed modulation system for modulating a transmitted orreceived signal in a ridged waveguide comprising; a dipole antenna;means mounting said antenna at one end'of said waveguide, one of theelements of said antenna being electrically connected to said waveguide,the other element of said antenna being insulated therefrom; a variableimpedance device connected across said elements; and a modulatingvoltage impressed across said variable impedance device; whereby, avariation in the impedance of said variable impedance device isreflected into said antenna, thereby modulating said signal.

2. A modulation system comprising; a waveguide; a dipole antenna mountedat one end of said waveguide, one element ofsaid antenna beingelectrically connected to said waveguide, the other element of saidantenna being insulated therefrom; a variable impedance device connectedacross said waveguide and said other element; and a modulating signalimpressed across said variable impedance device.

3. The invention as defined in claim 2 wherein said waveguide is ridged.it

4. The invention as defined in claim 3 wherein said variable impedancedevice is a germanium welded contact crystal.

5. A modulating system comprising: an antenna feed consisting of aplurality of waveguides; a dipole antenna mounted adjacent one end ofeach of said waveguides, an element of each of said antennas beingelectrically connected to its associated waveguide, the other element ofsaid antennas being insulated therefrom; a variable impedance deviceconnected across each of said waveguides and said other element,respectively; and means for impressing a modulating signal across eachof said variable impedance devices.

6. The invention as defined in claim 5 wherein said waveguides areridged.

7. The invention as defined in claim '6 wherein said 4 variableimpedance devices are germanium welded contact crystals.

8. A modulation system for modulating a transmitted or received signalin a waveguide comprising: an antenna having two elements, meansconductively mounting one element of said antenna at one end of saidwaveguide, means insulatingly mounting the other element of said antennaat said end of said waveguide, a variable impedance device connectedacross said elements, and means for impressing a modulating voltageacross said variable impedance device whereby a variation in theimpedance of said variable impedance device is reflected into saidantenna thereby modulating said signal.

9. The system of claim 8 wherein said means insulatingly mounting theother element of said antenna comprises an insulating sleeve mounted insaid means conductively mounting the one element of said antenna.

10. The system as defined in claim 9 wherein said variable impedancedevice comprises a welded contact germanium diode.

11. The system of claim 10 wherein the height of the antenna'elementsand the spacing therebetween is a quarter wave length of said signal.

12. A modulation system for modulating a transmitted or received signalin a ridged waveguide comprising: a dipole antenna, first means forconductively mounting one element of said dipole antenna at one end ofsaid waveguide, second means for insulatingly mounting the other elementof said dipole antenna at said one end of said waveguide, a variableimpedance device connected across said elements, and means forimpressing a modulating voltage across said variable impedance devicewhereby a variation in the impedance of said variable impedance deviceis reflected into said antenna thereby modulating said signal.

13. The system of claim 12 wherein said second means comprises aninsulating sleeve mounted in said first means.

14. The system as defined in claim 13 wherein said variable impedancedevice comprises a welded contact germanium diode.

15. The system of claim 14 wherein the height of the antenna elementsand the spacing therebetween is a quarter wave length of said signal.

References Cited in the file of this patent UNITED STATES PATENTS2,414,376 Heim Jan. 14, 1947 2,539,594 Rhines et al. Jan. 30, 19512,605,413 Alvarez July 29, 1952 2,669,694 Vogeley et a1. Feb. 16, 1954

